WDXS32 PGTW 291500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 22S (HALIMA) WARNING
NR 013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
INITIAL POSITION: 21.4S 82.5E
INITIAL INTENSITY: 45 KTS
GEOGRAPHIC REFERENCE: 1035 NM SOUTH-SOUTHEAST OF DIEGO GARCIA
MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 04 KTS
SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
DUE TO THE VIGOROUS POLEWARD OUTFLOW, LOW VERTICAL WIND SHEAR AND
WARM SST, TC 22S HAS REMAINED RESILIENT FENDING OFF SIGNIFICANT DRY
AIR SURROUNDING THE CORE CONVECTION. ANIMATED ENHANCED INFRARED
(EIR) SATELLITE IMAGERY DEPICTS PERSISTENT DEEP CONVECTIVE BANDING
OVER THE SOUTHERN SEMICIRCLE WRAPPING INTO THE WESTERN QUADRANT. A
291202Z 89GHZ MICROWAVE IMAGE SHOWS EXTENSIVE EXPOSED SHALLOW
RAINBANDS SURROUNDING THE WELL-ORGANIZED DEEP CONVECTIVE CORE. THE
GMI 37GHZ COLOR COMPOSITE MICROWAVE IMAGE REVEALS TIGHTLY-CURVED
BANDING WRAPPING INTO A WELL-DEFINED LOW-LEVEL CIRCULATION CENTER,
WHICH SUPPORTS THE INITIAL POSITION WITH HIGH CONFIDENCE. THE
INITIAL INTENSITY OF 45 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED
ON THE HIGH END OF DVORAK ESTIMATES, WHICH IS CONSISTENT WITH THE
OVERALL CONVECTIVE STRUCTURE.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK

CURRENT STEERING MECHANISM: COMPETING STEERING ENVIRONMENT WITH A
STRONG STEERING RIDGE TO THE WEST AND SOUTHWEST AND AN EXTENSION OF
THE NEAR-EQUATORIAL RIDGE TO THE NORTHEAST AND EAST

AGENCY DVORAK AND AUTOMATED FIXES:
PGTW: T2.5 - 35 KTS
FMEE: T3.0 - 45 KTS
FIMP: T3.0 - 45 KTS
CIMSS SATCON: 39 KTS AT 290837Z
CIMSS ADT: 32 KTS AT 290915Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
VWS: 5-10 KTS
SST: 26-27 CELSIUS
OUTFLOW: STRONG POLEWARD
OTHER FACTORS: VERY DRY ENVIRONMENT SURROUNDING THE SYSTEM

ANALYSIS CONFIDENCE:
INITIAL POSITION: HIGH
INITIAL INTENSITY: HIGH
INITIAL WIND RADII: MEDIUM

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TC 22S IS ESSENTIALLY BOXED IN WITH RIDGING
OVER THE WESTERN AND EASTERN SEMICIRCLES AS WELL AS A STRONG
LOW-LEVEL HIGH POSITIONED TO THE SOUTH. THERE IS NO CLEAR, DOMINANT
STEERING FEATURE THUS THE SYSTEM IS DRIFTING SLOWLY EQUATORWARD IN
AN ERRATIC FASHION. THIS TRACK MOTION IS EXPECTED TO PERSIST
THROUGH TAU 48 UNTIL A STRONG EAST-WEST ORIENTED RIDGE BUILDS IN TO
THE SOUTH AND INDUCES A WESTWARD TRACK TURN AND EVENTUAL
ACCELERATION WESTWARD AFTER THE FORECAST PERIOD. TC 22S SHOULD
REMAIN COCOONED THROUGH TAU 12 MAINTAINING AN INTENSITY OF 45 KNOTS
BEFORE SUCCUMBING TO THE DRY AIR ENTRAINMENT, WHICH WILL LEAD TO A
GRADUAL DECREASE IN INTENSITY THROUGH THE FORECAST PERIOD WITH
DISSIPATION EXPECTED BETWEEN TAU 60 AND TAU 72. NEAR TAU 60, A
STRONG UPPER-LEVEL TROUGH WILL DIG OVER THE SYSTEM WITH INCREASING
VERTICAL WIND SHEAR (25-30 KNOTS) ASSOCIATED WITH STRONG WESTERLY
FLOW LEADING TO THE SYSTEM'S DEMISE BY TAU 72.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT
WITH THE GENERALLY NORTHWARD, SLOW TRACK THROUGH TAU 24 BUT DIVERGES
AFTER TAU 24 WITH SIGNIFICANT DIFFERENCES IN THE TRACK AND TIMING
OF THE WESTWARD TURN. FOR EXAMPLE, NAVGEM AND GFS INDICATE A
SHARPER WESTWARD TURN AFTER TAU 48 WHILE THE BULK OF THE GUIDANCE
SHOWS A MORE GRADUAL WESTWARD TURN. THUS CONFIDENCE IN THE JTWC
FORECAST TRACK IS MEDIUM. THE JTWC INTENSITY GUIDANCE IS ALSO IN
FAIR AGREEMENT WITH COAMPS-TC (GFS VERSION) INDICATING A SLIGHT
INTENSIFICATION TREND WITH A PEAK INTENSITY OF 51 KNOTS BEFORE
STEADILY WEAKENING. HWRF WEAKENS THE SYSTEM QUICKLY TO 30-35 KNOTS,
WHICH IT MAINTAINS THROUGH THE FORECAST PERIOD. THE JTWC INTENSITY
CONSENSUS (ICNW) IS FLAT AT 45 KNOTS THROUGH TAU 36 THEN INDICATES
STEADY WEAKENING.

FORECAST CONFIDENCE:
TRACK 0 - 72 HR: MEDIUM
INTENSITY 0 - 72 HR: MEDIUM//
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